Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by internal combustion (IC) engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3).
Generally, an exhaust reductant (e.g., a diesel exhaust fluid such as urea) is injected into the aftertreatment system and mixed with the exhaust gas. The exhaust reductant can provide a source of ammonia to facilitate at least partial reduction of the NOx gases included in the exhaust gas. The reduction byproducts of the exhaust gas are then fluidly or fluidically communicated to the catalyst included in the SCR aftertreatment system. The catalyst decomposes substantially all of the NOx gases into relatively harmless byproducts, which are expelled out of such conventional SCR aftertreatment systems.
Hydraulic systems are generally used to pump the liquid exhaust reductant into the SCR system. In conventional hydraulic systems, the exhaust reductant (e.g., a diesel exhaust fluid such as urea) can crystallize at the tip of a doser or nozzle configured to communicate the exhaust reductant into the SCR system. This restricts gas flow in a pressure line coupled to the nozzle, which results in substantial negative pressure and high vacuum. The high vacuum is equalized by pulling exhaust reductant from an exhaust reductant storage tank instantaneously after completion of a purge of the system.
During purge, the system is filled with warm gas from the vehicle's exhaust system. In cold weather conditions, after shutdown, the warm purge gas cools downs, leading to volume shrinkage. This creates a negative pressure drawing exhaust reductant from the storage tank into the pump after system shutdown. The exhaust reductant can freeze in the pump. The fluid's expansion when frozen can then lead to pump malfunctions and/or cracks.